The present invention relates to a seat belt apparatus which is incorporated in a seat in an automobile or other transportation means, so as to restrain the passenger in order to protect the same upon occurrence of abnormal condition such as collision between vehicles or the like, and in particular to a seat belt apparatus incorporating a pretensioner which pulls a buckle engaged with the tongue toward the vehicle body side so as to fasten the seat belt in order to inhibit the passenger from moving forward upon abrupt deceleration caused by occurrence of an abnormal condition such as collision between vehicles or the like.
At present, a seat belt apparatus is incorporated in a seat in an automobile or other transportation means in order to protect the passenger upon occurrence of an emergency condition such as collision between vehicles or the like. The seat belt apparatus of such a kind incorporates, in general, a tongue attached to the seat belt, and a buckle device to which the tongue is locked, and by engaging and disengaging between the tongue and the buckle device, the seat belt can be simply worn or taken off.
Further, in such a seat belt apparatus, the seat belt is wound on a wind-up reel in a retractor by a relatively weak force, and accordingly, the seat belt is freely pulled out normally so that no oppression is exerted to the passenger since the wind-up force of the retractor is relatively weak. Further, by locking the rotation of the wind-up reel in the pay-out direction of the seat belt upon abrupt deceleration of a vehicle caused by collision between vehicles or the like, the forward movement of the passenger is inhibited.
By the way, in a conventional seat belt apparatus, the seat belt is slightly paid off due to further fastening of the seat belt by wind-up upon locking the rotation of the wind-up reel in the case of abrupt deceleration. Further, since the seat belt is likely to be relatively loosely worn, the seat belt is normally slack, and further since it is pulled by the inertia force of the passenger, the seat belt is elongated by a slight degree. Due to such pay-out, slack and elongation of the seat Pelt, the passenger is moved forward upon deceleration, and accordingly, it is sometimes impossible to restrain the passenger.
Accordingly, seat belt apparatuses incorporating a pretensioner have been developed, in which the pretensioner is operated upon abrupt acceleration so as to pull the buckle device in order to fasten the seat belt, thereby it is possible to inhibit the passenger from being moved forward, in a more positive manner.
As the pretensioner, there has been developed a pretensioner such that reactive gas is generated upon deceleration, and a piston is operated by the gas thus generated to fasten the seat belt. The pretensioner actuated by the reactive gas can be formed in a relatively simple manner, and it can be rapidly respond upon necessity to rapidly fasten the seat belt.
Further, there is provided a pretensioner using a spring as a drive source for actuating the pretensioner.
However, in such a pretensioner, a large acceleration is at first produced in the pulling direction of the pretensioner since the buckle device is pulled abruptly by a predetermined degree upon operation, and a predetermined deceleration is produced after the movement of the buckle device by the predetermined degree. Accordingly, the actuating member which is adapted to release the engagement with the tongue provided to the buckle device is moved in the releasing direction by its inertia, and therefore, there is a risk of releasing the engagement with the tongue.
Accordingly, Japanese Laid-Open Patent Publication No. 3-208752 discloses a belt lock for a safety system in which during the operation of the pretensioner, when a large deceleration acts upon the buckle device during the operation of the pretensioner, tile engagement between the tongue and the latch member in tile buckle device is prevented from being released, by restraining the actuating member from moving in the releasing direction. This belt lock has a lever which is swingably supported at its intermediate part to the housing, and which is provided at one end with a compensating weight and is coupled at the other end, relatively rotatably to the actuating member so that when the actuating member tends to move in the releasing direction by an inertia upon occurrence of a large deceleration, a force in a direction opposite to the direction of the inertia force acting upon the actuating member is applied to the actuating member through the intermediary of the lever by the inertia force acting upon the compensating weight in order to restrain the actuating member from moving in the releasing direction.
Accordingly, the engagement between the tongue and the buckle device is prevented during the operation of the pretensioner.
However, with such a belt lock in the safety belt system, since the inertia force acting upon the compensating mass has to cope with the inertia force of the actuating member, the compensating mass should be made to be large. Accordingly, the weight of the belt lock becomes large. Further, although it is possible to decrease the compensating mass, the lever ratio should be made large in this case, and accordingly, the length of the lever on the compensating mass side has to be relatively large. Thus, the belt lock becomes large.
Further, in the case in which the compensating mass is increased or the length of the lever on the compensating side is increased, since the lever is coupled to the actuating member, this compensating mass should be swung upon normal releasing operation of the actuating member, and accordingly, a relatively large force is required, resulting in heavy manipulation touch and in unsatisfactory manipulation feeling.
Further, since the large compensating mass should be swung, not only the strengths of the support shaft for supporting the lever and the coupling part between the other end of the lever and the actuating member should be ensured up to certain degrees, but also the relative motion between the lever and support shaft and the relative motion between the other end of the lever and the actuating member should be made to be smooth. Accordingly, it is necessary to increase the degree of accuracy in process and assembly so that the cost thereof becomes high.
Further, since a force caused by the inertia force acting upon the compensating mass acts upon the actuating only in a direction opposite to the inertia force of the actuating member, a case such that the movement of the actuating member cannot be surely inhibited, sometimes occurs.
The present invention is devised in view of the above-mentioned problems, and accordingly, one object of the present invention is to provide buckle device in a seat belt apparatus which can surely inhibit the actuating member from moving in the releasing direction upon operation of the pretensioner, and which can be formed to be compact and cheap, and which can offer a satisfactory manipulation feeling.